The inventive concept relates to a Mission Critical Push to Talk (MCPTT) service, and more particularly, to a method of controlling a floor of an MCPTT group performing the MCPTT service in an off-network.
Recently, special purpose-communication systems for public safety, transportation, and public utilities and industries are being studied. These special purpose-communication systems have to provide group communication services such as Push-to-Talk (PTT) and support services in disaster situations where a communication infrastructure is not supported. An MCPTT service based on 3rd Generation Partnership Project (3GPP) guarantees a PTT service through direct communication between terminals when a base station and a server cannot function, i.e., in an off-network situation, and describes protocols related to floor control so that the floor control can be performed without a arbitration server.